Author Topic: Continental.GT 535 converting to Mikuni Carburetor  (Read 192 times)

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Bess_GT

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on: November 09, 2019, 03:48:55 PM
Hi all, This is my first post here. But I've been a frequent visitor here for past few months and I've learned many things from this forum. I'm a newbie in mechanics.

I'm trying to convert the EFI(failed one now, the bike was sitting for many years.) to carburetor and after a hard search out, I got this Mikuni carb from a guy. But I don't know how the carburetor fits in the slot. Please see the attached pics. I'm trying to use the stock Flange and the carburetor is getting stuck between the bars holding the cylinder head assy.

I've seen Otto_Ing(Paul)'s video of the same, but not sure how he did it. Also there are few replies in some posts here about this, but couldn't find anything about this issue.
Earlier I made a quote for conversion kit to Hitchcock, but the Pound to INR conversion makes it much above my budget.

Thanks.
P.S. I've been on this for many months, trying to open the failed fuel pump motor, made it rotate but the pressure in the motor varied after sealing. Trying a second hand fuel pump motor of RE500, which failed after few kms.
« Last Edit: November 09, 2019, 03:51:20 PM by Bess_GT »


ace.cafe

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Reply #1 on: November 09, 2019, 04:06:50 PM
You will need to do some fabrication/modification to make things fit.

There is no fuel pump in the carb system. You need a petcock adapter plate to replace the fuel pump at the tank, and use gravity feed for fuel.
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Bess_GT

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Reply #2 on: November 09, 2019, 04:41:19 PM
Hi ace.cafe,
But the bars that support the cylinder head is blocking the top of carburetor(as marked in pic) . May i know how i could modify that?
« Last Edit: November 09, 2019, 05:20:01 PM by Bess_GT »


gizzo

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Reply #3 on: November 09, 2019, 06:57:25 PM
Looks like you'll have to notch the bracket with a grinder to make room for the carb to move in enough. Try making some cardboard templates to figure out where to cut, before you cut the real ones.  Or,  find a piece of tube fits in the stub and use that, and another piece of rubber hose, to move the carb out a little bit. That's probably a less ideal but maybe easier solution. Good luck man, big project for someone just learning to be a mechanic.
« Last Edit: November 10, 2019, 12:20:43 PM by gizzo »
simon from south Australia
Continental GT
Pantah
Monster
DR250
DRZ400SM


Bess_GT

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Reply #4 on: November 10, 2019, 04:04:55 AM
Thanks gizzo. Yes exactly that is the issue. I've confirmed this with the Paul's video. https://youtu.be/d4RRMA-r3wY
That is a different bracket.
I will check from where this bracket can be found(also asked Paul in comment)?No lathe at home, hence it would be hard to build new one or grind the existing.


gizzo

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Reply #5 on: November 10, 2019, 12:28:32 PM
No angle grinder, holesaw or files?
simon from south Australia
Continental GT
Pantah
Monster
DR250
DRZ400SM


Bess_GT

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Reply #6 on: November 10, 2019, 03:50:02 PM
Nope gizzo. Got a hacksaw blade..but not sure it will cut this metal, but i'll try. May be i will take it to lathe if that don't work.
Paul replied that the head stay bracket came with the hitchcock kit.


ace.cafe

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Reply #7 on: November 10, 2019, 09:48:11 PM
Cut the bracket to fit the carb, or maybe extend the inlet manifold if there is the ability to get better fit like that.

It is generally necessary to have tools and some experience to get into a modification process. Getting those would be the first step before starting modifications.
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Adrian II

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Reply #8 on: November 10, 2019, 10:19:58 PM
Quote
I got this Mikuni carb from a guy.

What size? (The carb, not the guy.) What was if fitted to before, this could be important as the settings might need to be changed (different jets, needle, slide, etc).

A.
Grumpy Brit still seeking 500 AVL Bullet perfection! Will let you know if I get anywhere near...


gizzo

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Reply #9 on: November 11, 2019, 04:00:01 AM

It is generally necessary to have tools and some experience to get into a modification process. Getting those would be the first step before starting modifications.

This Δ . You're going to have to invest in a few fabricating tools if you want to be doing that sort of work. They don't have to cost a lot of money. Go on, it'll be fun.

How are you going to notch the brackets in the lathe? Does it have a milling attachment? I've always wanted to have a go on one of those to see how good a job of milling they can do.
simon from south Australia
Continental GT
Pantah
Monster
DR250
DRZ400SM


Bess_GT

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Reply #10 on: November 11, 2019, 05:38:34 AM
ace.cafe : tried connecting it with inlet manifold, but it seems the carb is far too behind. Pls see attached pic (carb-fit).

 Adrian II: Hi, thats what confusing me. The size of the carb is the diameter of the end that connects to manifold? I measured using a scale and its around 32mm. There is a number in main jet like 7 47.5. The bowl has a number 24(pls see attached pic of bowl). Does carb size vary according to engine capacity?is it the diameted or the jet capacity?

gizzo: removed the bracket, pls see attached pic (carb fit). Only left end bracket need to be altered.

New issues: the lock in the flange need to be removed using a blade as its not the size of carb(pic flange-lock)
The throttle cable that came with the carb is having a smaller button lock that will loose out from the plastic hole.  (Pic cable button lock). But i think it could be worked around..not sure though..


Adrian II

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Reply #11 on: November 11, 2019, 12:39:58 PM
What you have is a Mikuni VM series carb, they come in all sizes from 22 to 44mm. What I mean by size is the bore of the instrument where the air flows through over the jets. So if the INSIDE diameter of the spigot where it sits in the rubber mounting is 32mm you have a VM32, actually not a bad size for a lightly tuned Bullet.

Ignore the number stamped inside the float bowl. Now because these carbs are used on lots of different bikes, some with two-stroke engines, two outwardly identical carbs can be set up very differently, one would make the engine run very nicely, the other wouldn't work at all well.

Fortunately some folks on here are running with VM32s, if you search the forum archives someone will have posted this information - hang on, it's here. Just be careful NOT to follow the recommendations for a Mikuni TM32, this is a different type of carburetor from the VM32.

https://forum.classicmotorworks.com/index.php?topic=16053.0;all

As for getting the carb to fit the head without fouling the head steady brackets, try a spacer cut from 1/4" Tufnol to move the carb mounting rubber out a bit instead of butchering the brackets. The mounting holes are 60mm centers, 6mm bore, the hole in the middle will need to match the bore of the carb you're using.

A.


Grumpy Brit still seeking 500 AVL Bullet perfection! Will let you know if I get anywhere near...


Bess_GT

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Reply #12 on: November 11, 2019, 03:36:00 PM
Thanks Adrian II. I think it'll take a bit time for me with the carb to understand the tuning set up described in the link. Yeh, the inside diameter is around 32mm. Correct me if I'm wrong, higher the cylinder capacity higher the spigot diameter and jet sizes right?
I made a bracket from a nearby sheet metal store(attached pic) which suited well (but not sure it affects the engineering, but i think the whole frame was not designed for this engine because there is a small bit that help in extending the head stay screw, it shouldn't be there it seems)
Remaining work: 1. a button that need to be welded/moulded to the end of the carb throttle cable(i think the RE carb cable comes with this button, but this cable is japan made(wriiten) and don't want to waste it)
2. A cable free play nut at the accelerator end as there isn't a free play other than carb top pipe screw.
3.I'm thinking of attaching a rounded steel sheet  to connect air filter box to carb. Couldn't find similar rubber hose with length and also i think steel supports the carburetor too(as it is only holding on to the rubber flange)